Studies on the mechanisms involved in lipid accumulation in mammalian cells will be continued. The effect of membrane lipid modifications on the function of membrane-bound enzymes and transport systems will be continued. These will involve substances that enter cells through carrier mediated transport as well as those that enter by diffusion. The temporal relationship between diet-induced changes in ascites fluid lipoprotein and cellular fatty acid composition will be investigated. Additional work wll be done to elucidate the mechanism of the observed increase in Ehrlich cell cholesterol content when saturated fatty acids are fed to the mice in which the cells are grown. The properties of the cholesterol metabolizing enzymes of the cells will be examined, particularly with respect to possible effect of membrane fatty acid composition. Attempts will be made to solubilize these enzymes and reconstitute them in phospholipid vesicles, with emphasis on the role of membrane lipid composition on enzyme function and regulation. Emphasis will be placed on the microsomal acylcoenzyme A: cholesterol acyltransferase, the enzyme thought to be responsible for the intracellular synthesis of of cholesteryl esters. An attempt also will be made to devise tissue culture systems that will allow more specific modification of Ehrlich cell membrane lipid composition. Finally, attempts will be made to devise isolated membrane and reconstituted liposome systems suitable for study of the fatty acid transport mechanism. BIBLIOGRAPHIC REFERENCES: McGee, R., Brenneman, D.E. and Spector, A.A. 1977. Regulation of fatty acid biosynthesis in Ehrlich cells by ascites tumor plasma lipoproteins. Lipids 12:66-74. Brenneman, D. E., Kaduce, T. and Spector, A.A. 1977. Effect of dietary fat saturation on acylcoenzyme A: cholesterol acyltransferase activity of Ehrlich cell microsome. J. Lipid Res., in press.